The present invention relates to an image processing system, and more particularly to a game computer system processing both moving and still pictures.
In a conventional image processing system, image data stored in an external storage such as a CD-ROM, are read to be displayed on a video screen by a video encoder unit. According to this system, a memory is necessary to have a capacity for storing at least one screen data to control the video screen vertically.
In a conventional game computer, background (BG) and sprite pictures are combined on a screen to display one image. The background and sprite images are composed of plural elements, which are called characters and sprites, respectively. The background image is defined on the screen by its position, color and pattern for each character. The position of each character is defined by its coordinate. The game computer is provided with a memory, from which a virtual screen is derived so that the virtual screen is taken to have an area larger than the real screen (CRT). The real screen is scrolled by shifting a picture on the virtual screen.
The computer has a video-RAM (VRAM), which includes a background attribute table (BAT) and a character generator (CG), as shown in FIG. 1. In accordance with data in the background attribute table (BAT) and character generator (CG), the background image is managed.
In such a game computer system, plural pictures arranged at different angles are displayed successively in a predetermined order whereby the BG screen seems rotating. In some cases, such plural pictures are formed arithmetically in accordance with a matrix coordinate, as shown in FIG. 2.
In the conventional game computer system, a VRAM stores image data at once, and then a video controller VDC reads and processes the image data. The VDC supplies the processed image data to a video encoder unit VDE, so that a CRT displays the image data, as shown in FIGS. 3 and 4. Basically, the image data are processed for each screen, and therefore, the VRAM must store at least image data for one screen prior to the processing.
In the case of a moving picture, it is not necessary to store the entirety of the image data in a VRAM, as shown in FIG. 5A, because a moving picture is composed of different images for each field. That is, image data are transmitted not through the VRAM to the video encoder unit VDE, as shown in FIG. 5B. Therefore, image data for a moving picture must be stored in an external storage before the display thereof. This system may not perform special processing, such as rotation, reduction and extension. If image data for a moving picture are stored in the VRAM at once, the transmission of the image data is delayed by one field. Eventually, when a computer system deals both with moving and still pictures, one of the two may not be displayed well.
Generally, a game computer is required to deal with a large amount of data to display a video image. For instance, when a game computer employs a color display monitor of 512.times.512 dots, in which each luminance of RGB is defined by eight bits, each color image needs a memory capacity of about 768 k bytes (512.times.512.times.3). In a game computer, predetermined data must be processed while tens of images are displayed in one second, and therefore, image processing must be performed in a horizontal (HSYNC) period. For that reason, according to the conventional game computer, it is difficult to realize special graphic processing such as rotation, magnification, reduction and the like.